1. Field of the Invention
The invention relates to a plain bearing element comprising a single-layer or multilayer metallic bearing material, pockets for lubricating oil being provided in the sliding surface. The term "plain bearing elements" is intended to mean, among others, plain bearing half-liners, flanged bearings, bushes and thrust washers, comprising a single-layer or multilayer metallic bearing material which may be deposited on a backing material.
2. Description of Related Art
Provision of depressions on the sliding surface has been known for years. It is suggested in DE-PS 546 781 to make, for the avoidance of "contact oxidation", in one of the contacting surfaces of a bearing discontinuities, depressions, roughenings and similar means. In this connection also circular depressions were shown but it is not stated how these depressions are dimensioned, arranged or lined.
DE-PS 834 480 describes a bearing in which the bearing surface is composed of a plurality of small areas of hard and soft bearing material. Apart from groove-shaped depressions also square-shaped recesses are provided which are, however, completely filled with a soft bearing material. The depressions are made by means of an embossing roll rotating in a metallic bath.
From DE-OS 27 11 983 is known a bearing which has, in addition to oil grooves, also hemispherical oil recesses of a diameter of 1.5 to 2.5 mm which are arranged with a spacing of 4 mm in circumferential direction or 4.8 mm in axial direction. Because the thickness of the bearing alloy is only 0.25 mm these oil recesses extend up to the steel backing. The lubricating oil pockets of these dimensions have, among others, the disadvantage that the bonding region of the bearing alloy with the steel backing is exposed so that delaminations may occur in this region.
From DE 33 26 316 C2 are known bearing bushes of sintered metal with lubricating oil pockets arranged on the inner sliding surface, the pockets being hemispherical or ellipsoidal. The depth of the oil pockets is 0.2 to 1 mm while 10 to 30% of the entire sliding surface is occupied by the oil pockets.
AU 143 992 shows a sliding surface design with embossed recesses which are entirely filled with a soft plain bearing material.
DE-GM 7817118 describes self-lubricating bearing which has for the embedding of a solid lubricant cavities of circular or spherical shape.
From U.S. Pat. No. 5,462,362 is known a sliding element used for extremely low sliding velocities such as spherical elements in artificial joints. The sliding surface has cylindrical recesses whose diameter is 0.2 to 0.8 mm and depth is 1 to 10 .mu.m. The recesses are also filled with a solid lubricant.
These known bearing elements may be used, depending on the bearing material, only for low sliding velocities of up to about 5 m/s and average loading of up to about 30 MPa. The bearing elements are not suitable for use as big-end bearings and main bearings in internal-combustion engines because due to the relatively large depth and/or the large area occupied by the oil pockets the build up of the hydrodynamic pressure needed for these applications is not possible to a sufficient degree.
Also known are bearing elements according to EP-PS 104159 and U.S. Pat. No. 5,238,311 which have groove-shaped recesses in the sliding surface whose depth is 3 to 6 .mu.m. These elements have the disadvantage that when the grooves are subjected to the loadings of over 30 MPa which is common in big-end bearings and main bearings of internal-combustion engines, they are either plastically deformed or worn which may lead to seizure so that they may no longer perform their task.
The groove bearings described in EP-PS 57808 which comprise grooves filled with soft bearing materials have, in practice, the disadvantage that after a certain time of operation the soft bearing material if flushed out by the lubricating oil and the bearing is no longer able to function.